The present invention relates to methods and systems for measuring the water level of a body of water, whether free flowing water such as a river or stream or stationary such as a lake, reservoir or holding tank, and, more particularly, to an improved water level measuring method and system which does not involve mounting of the measurement equipment over the water surface, i.e., which enables water level measurements to be made from the edge of the water, e.g., from an embankment, platform or bridge structure adjacent to the water.
Both mechanical and electromechanical devices are used to measure what is referred to as xe2x80x9cstagexe2x80x9d or water level with respect to a datum point. This is generally done from a bridge platform or structure in or over the water. Such water level measuring devices require that the sensor be in contact with water surface and in the majority of instances, require a specially built housing or enclosure, referred to as a stilling-well installation, to dampen or filter the turbulence of water in order to obtain a correct reading. Such stilling-well installations generally employ a long, typically two-foot diameter corrugated pipe attached vertically to an adjacent platform, and extending all of the way into a water column. All water level measurement instruments currently used by the United States Geological Survey (USGS) use the contact methods in determining water level and water flow, and, in this regard, there are nearly 7,000 sites throughout the United States which contain equipment or instruments for measuring water level.
With some devices, it is difficult to obtain a measurement of water level because of the lack of a platform or other structure for mounting the measuring equipment or instrument. Further, because the placement of such structures in parks and wildlife refuges detracts from the natural beauty of the environment, the structures are often located at sites which are out of the way and difficult to get to, and substantial time and expense is incurred in transporting personnel to visit, and make measurements at, these largely inaccessible sites. Moreover, there are many areas for which water level information is needed but cannot be obtained because of the cost and manpower necessary to prepare a site for installation of equipment. Further, because at least with USGS installations, a majority of the stage measuring instruments are mounted on bridge platforms, the installation of the instruments and extraction of the data can be hazardous.
Some prior art commercial systems use measuring or sensing beams and require that the sensing or measuring beam (which may be a radar beam or laser beam) be mounted such that the beam projects directly vertically downward to the water surface. Further, the characteristics of the measuring beam itself (e.g., whether in pulsed mode or continuous mode of operation) are employed in making the measurement, and this can often complicate the associated electronic circuitry required. In such systems, beam characteristics such as time-of-flight or change in phase are used in determining the water level, in contrast to the present invention which, as explained below, uses simple geometry in calculating the water level.
In accordance with the invention, a method and system are provided for the determination of the water level of both free flowing bodies of water (e.g., rivers or streams) and stationary bodies of water (e.g., lakes, reservoirs or holding tanks), which overcome or substantially eliminate the above-discussed problems associated with prior art methods and devices.
Among other important advantages thereof, the invention does not require the system apparatus be positioned vertically above the water surfaces, i.e., the apparatus need not be mounted on a structure (bridge or platform) which is located over or across the water but instead can be sited and operated at the edge of the body of water. Further, the invention can be used in measuring water levels in canyons, from bluffs and in highly inaccessible areas wherein a conventional water level measurement device would normally be positioned directly vertical with respect to the water surface. Further, as indicated below, the invention makes water level measurements based on simple geometry, i.e., uses no electronic or electromechanical or mechanical contact of a sensor with the water surface, and thus eliminates the problems associated with contact systems, such as damage to the sensor caused by floating or submerged objects in free flowing water. In addition, installation of the invention at new sites, which is done periodically by the USGS, can be carried out with substantial cost savings, because, inter alia, there is no need for stilling wells.
In accordance with a first aspect of the invention, a system is provided for determining the level of a body of water, whether free flowing or stationary, the system comprising: a rotatable reflective element including an inclined reflective surface; a light source for directing a light beam along a first path onto the reflective surface so that the beam is reflected from that surface and redirected along a further path; a motor for rotating the reflective element so that the redirected beam is scanned and so that, during scanning thereof, the redirected beam is directed onto the surface of the body of water such that at least a portion of the redirected beam is reflected from the surface as a reflected beam; an optical detector array, located at a determined distance from the reflective element on the opposite side of the body of water from the reflective element and in a common horizontal plane with the reflective element, for receiving the reflected beam and for producing an output in response thereto; and controller means for receiving the output of said optical detector array, for determining, based on said output, the scan angle of the beam with respect to true vertical, and for calculating, based on the determined scan angle and the determined distance between the reflective element and the optical detector array, the distance from the common horizontal plane to the water surface so as to determine the water level.
Preferably, the controller means includes a controller for receiving the array output and for producing a corresponding control signal, and a counter controlled by said controller for, responsive to receiving the control signal, producing a scan angle count related to the scan angle. The controller means preferably further comprises an optical detector positioned with respect to the reflective element for receiving the redirected beam during scanning thereof and for, responsive to receiving the redirected beam, transmitting a start signal to the counter to initiate the scan angle count. Advantageously, the optical detector is positioned vertically beneath the reflective element so as to receive the redirected beam when the beam is directed vertically downward during scanning thereof.
In a preferred implementation, the detector array produces a further output responsive to receipt thereby of the redirected beam as reflected from the reflective element along a horizontal path in said common plane, and the controller, responsive to receiving the further output, produces a further control signal for the counter so that the counter produces a further count related to the time required for scanning rotation of the beam between vertical and horizontal positions. The controller means then divides the further count by 90 to produce a value of degrees per count and multiplies the scan angle count by said value to produce a scan angle value.
In one preferred embodiment, the controller is located on the opposite side of the body of water and the control means transmits its control signals to the counter across the body of water. In one implementation of this embodiment, the control means further comprises a further light source connected to the controller for producing light signals based on the control signals and an optical detector connected to the counter for receiving the light signals and converting the light signals into count control signals for the counter. In an alternative implementation, the control means further comprises an r.f. modem connected to the controller for producing r.f. signals based on the control signals and an r.f. modem receiver connected to the counter for receiving the r.f. signals and converting the r.f. signals into count control signals for the counter.
Advantageously, the reflective element is mounted on a motor shaft having a substantially horizontal longitudinal axis and the reflective surface is inclined at an angle of 45xc2x0 to that longitudinal axis. Preferably, the light source comprises a laser. The motor preferably comprises a continuously rotating motor for providing continuous scanning of the redirected beam through 360xc2x0.
According to a further aspect of the invention, a method is provided for determining the level of a body of water, whether free flowing or stationary, the method comprising: scanning a laser beam reflected at a variable angle to true vertical from a rotatable reflective element located at an area adjacent to but spaced from the body of water, so that the beam is directed onto the surface of the body of water during scanning and that at least a portion of the beam is reflected from that surface; receiving the portion of the beam reflected from the surface with a detector array located on the opposite side of the body of water from, and in substantially the same horizontal plane as, said reflective element; determining the scan angle to true vertical at which the portion of the reflected beam is received by said detector array; and using (i) the scan angle to true vertical so determined, and (ii) the distance between the reflective element and the detector array, to calculate the distance from said horizontal plane to the water surface so as to determine the water level.
Preferably, the scan angle is determined using a controller to produce a control signal when the detector array receives the reflected beam, and a counter controlled by the controller for, responsive to receiving that control signal, producing a scan angle count related to the scan angle. Advantageously, an optical detector is positioned with respect to the reflective element so as to receive the beam during scanning thereof and a start signal is transmitted by the optical detector to the counter, responsive to receiving said beam, so as to initiate the scan angle count.
In a preferred implementation, the detector array is used to produce an output responsive to receipt thereby of a beam reflected from the reflective element along a horizontal path in the common horizontal plane and the controller, responsive to receiving this output, generates a further control signal for the counter so that the counter produces a further count related to the time required for scanning rotation of the beam between vertical and horizontal positions. This further count is divided by 90 to produce a value of degrees per count and the scan angle count is multiplied by this value to produce a scan angle value.
In one preferred implementation, the controller is located on the opposite side of the body of water with the array, and the control signals are transmitted to the counter across the body of water. In one embodiment of this implementation, a further laser, connected to the controller, is used to produce light signals based on the control signals and an optical detector, connected to the counter, is used to receive the light signals and to convert these light signals into a count control signal for the counter. In an alternative embodiment of this implementation, an r.f. modem, connected to the controller, is used to produce r.f. signals based on the control signals and an r.f. modem receiver, connected to the counter, is used to receive the r.f. signals and to convert these r.f. signals into count control signals for the counter.
Preferably, the laser beam is scanned by using a continuously rotating motor to continuously rotate the reflective element.
Further features and advantages of the present invention will be set forth in, or apparent from, the detailed description of preferred embodiments thereof which follows.